The fixed radio communications may operate using wire line or radio technology. Wire line technologies include utilizing the utility distribution lines and/or telephone lines. Wireless technologies may utilize the 902-928 MHz range, which can operate without a FCC license through the use of frequency hopping spread spectrum (FHSS) transmission, which spreads the transmitted energy over the band. According to FCC Regulations, for frequency hopping systems operating in the 902-928 MHz band, total output is as follows: 1 watt for systems employing at least 50 hopping channels; and, 0.25 watts for systems employing less than 50 hopping channels, but at least 25 hopping channels. See, 47 U.S.C. § 15.247.
FHSS systems meet the FCC specification by communicating to remote communication devices in synchronization, both in time and frequency. Using this approach, all devices know when to hop to the next channel in the sequence and what the next sequence channel is. A known FHSS system utilizes a hop rate that is faster than the data rate to send multiple sets of randomly selected frequencies in each message to distribute the transmitted energy over the communication band. This distribution is one of the FCC requirements to operate in the ISM band.
A disadvantage of the above is that it requires all devices to include a real time clock, which adds to the cost of the device. In addition, some type of battery storage system is required to maintain the real time clock in the event power should be removed from the device. Further, the requirement to step rapidly through the frequencies constrains the design of such devices and further limits cost reduction.
Another disadvantage of conventional FHSS systems is that they lack provisions to enhance data reliability. For example, U.S. Pat. No. 5,311,542, to Eder, discloses a spread spectrum communication system wherein segments of a message are broken into 20-bit segments. Each of the segments are transmitted over a different carrier signal within a frequency range of 902 to 928 MHz. However, the Eder system fails to teach a method to prevent lost segments or enhance data reliability should one or more of the segments not be received or carrier signals be blocked.
U.S. Pat. No. 5,311,541, to Sanderford, Jr., discloses another spread spectrum communications system. Sanderford, Jr. teaches a system whereby preamble information and message-data are sent via a psuedo-randomly selected single carrier frequency. Should the message not be received, another carrier frequency is selected and the entire message is retransmitted. While this provides a higher probability of a receiver receiving a complete message, the Sanderford, Jr. system must first sweep the spectrum to determine which channels are free of interference. After sweeping the spectrum, the receiver updates status information located in memory associated with each channel. Each of the receivers and transmitters communicate and store this data to prevent transmission on channels that are jammed or have interference. This disadvantageously increases the cost and complexity of the receiver, and requires the receivers/transmitters to periodically communicate this channel status data in order to maintain a higher level of reliability.
Therefore, there is a need for a FHSS communication device that is cost efficient, meets FCC requirements for power distribution in the ISM band, and includes provisions for data integrity. The present invention is directed to these, as well as other, needs in the art.